When I searched eBay for Coles $30 freebie, nothing came up.
The link you provided [which I have now deleted] had the date Aug 20 in it and was only valid for 14 days.
Did you notice that you don’t get the $30 discount until your free period is over, you have started the eBay Plus membership, AND you have spent a minimum of $80. So what does it actually cost to get $30 off?
The current eBay + special is 5% off and you get free delivery on orders over $49. The speed of delivery is not mentioned. Perhaps it is a seperate fulfilment channel to the normal Coles on-line, or perhaps it has to go through more hoops to get to the on-line system.
They do seem to have a range of food and drinks on offer.
What I am uncertain about is what is the benefit of buying through eBay Plus vs directly from Coles. You would need to price a basket of shopping for both and then add any applicable delivery fee to see which works out best.